Radio apparatus



18, 1934. i c. D. HAIGIS RADIO APPARATUS v I Filed Marcfi" 4. 19 31 Patented Sept. 18, 1934 UNITED STATES PATENT- @FFWE 1,974,184" I v RADIO APPARATUS Delaware Application March 4, 1931, Serial No. 520,058

10 Claims.

My invention relates to radio apparatus and it has particular relation to radio transmitting and receiving systems of the duplex type.

In my copending application, Serial No. 509,156,

filed January 16, 1931 and assigned to RCA Victor Company, Inc., I have disclosed an improved super-regenerative receiving system particularly adapted to the reception of radio signals at ultrahigh frequencies. I have further pointed out, in the application referred to, that my new receiving system, without shifting the coupling between it and an antenna normally used for reception, also may be utilized to transmit signals if suitable means such as change-over switches are employed whereby a modulator tube may be coupled to the output circuit.

The manipulation of change-over switches, however, interferes with true duplex operation and it is, accordingly, an object of my present 0 invention to provide means whereby such switches are not required.

Another object of my invention is to provide a radio signaling system particularly adapted to duplex operation at ultra-high frequencies.

Another object of my invention is to provide a combinedsuper-regenerative receiver and transmitter that shall be extremely stable in operation.

An additional object of my invention is to provide, in a duplex signaling system, means to prevent inter-action between portions thereof used in the transmission of signals and other portions used in the reception of signals.

A still further object of my invention is to provide, in a system of the type described, means whereby the transmission of signals shall not cause interference with the reception of signals from a distant station.

The aforementioned objects and other objects appurtenant thereto I prefer to accomplish by providing a signaling system wherein the circuits carrying radio frequency currents are electrically symmetrical with respect to ground, and I purposely maintain a portion of the system so strongly oscillating at the frequency at which duplex operation is desired that parasitic oscillations are ineffective to impair signal reception or transmission. I also provide means whereby the generated oscillations may be prevented, periodically, from attaining too great an amplitude and I associate a modulating and an amplifying device with the output circuit of the oscillatory portion of the system through a balanced bridge whereby the system may be used, without interrupting the continuity of the generated oscillations, for either the reception or the transmission of signals.

The novel features that I consider characteristic of my invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and its method of operation, together with additional objectsand advantages thereof, will best be understood from the following description of a specific embodiment, when read in connection with the accompanying drawing.

The single figure of the drawing is a diagrammatic view of a duplex signaling system constructed and arranged according to my invention.

Referring specifically to the drawing, a radio receiver, comprising a preferred embodiment of my invention, includes an oscillation generator constituted by a plurality of thermionic devices 1 and 3, which may be of the three-electrode type, each having a cathode 5, a grid 7, and a plate 9.

The several thermionic devices are disposed in push-pull relation insofar as their input and output circuits, carrying currents at radio frequencies, are concerned. In other words, the devices are provided with a common input circuit constituted by an inductor 11 having a plurality of serial-1y connected, adjustable condensers 12 disposed in shunt thereto, the terminals of the said inductor being connected to the grids, respectively, of the said thermionic devices. The rotors of the tuning condensers are provided with a ground connection 13, whereby the input circuit is rendered electrically symmetrical with respect to ground. The condensers 12 are preferably, but not necessarily, simultaneously adjustable.

An intermediate point 14 on the input inductor is connected, through a grid condenser 15 and a manually operable switching device 16, to the cathode circuit of the tubes. -The switching device and its function hereinafter will be referred to again.

A preferred antenna system is constituted by two straight wires 17 that extend in opposite directions from the ends of a coupling coil 18 disposed within the inductor 11. The overall length of the antenna is not critical, For best results at any given frequency, however, it is desirable that a current loop be established at the mid-point of the coil 18. The mid-point of the coil may or may not be provided with a ground connection 19. Hence the same is shown in dotted .lines to indicate its location if used.

Biasing potential for the tubes is supplied over an adjustable grid leak 20, one terminal of wh ch is connected to the intermediate point 14 on the input inductor, and the other terminal of which fying tube is may be connected to the movable arm of a potentiometer 21 disposed in shunt relation to a grid biasing battery 23, or the said terminal may be connected directly to the negative pole of the said battery, if desired.

The cathodes of the thermionic tubes are provided with a common ground connection 25.

The radio frequency output circuit of the oscillator stage is constituted by an inductor 2'7 shunted by a plurality of adjustable tuning condensers 29 connected in series, the rotors of which are provided with a ground connection 31 to render the circuit electrically symmetrical. The condensers 29 are preferably, but not necessarily, simultaneously adjustable.

The input and output circuits may, without de-' parting from the spirit of my invention, take other forms most suited to the frequencies it is desired to receive. For example, at extremely high frequencies the tuning condensers 12 and 29 may be omitted and tuning may be accomplished by symmetrically varying the inductance of each of the coils 11 and 27, in any convenient way. It also lies within the scope of my invention to inductively couple the inductors 11 and 27 in either a positive or negative sense.

Plate potential for the tubes 1 and 3 is supplied from a plate potential source 33 over a circuit including a choke coil 35, which constitutes one arm of a Wheatstone bridge 36, the remaining arms of the bridge being constituted, respectively, by similar choke coils 37, 39, and 41.

Preferably, the point upon the output inductor 27, to which is connected the conductor supplying fplate potential, is located at the electrical center of the inductor.

A by-pass condenser 42 is connected in shunt to the plate potential source and theprimary winding of the audio frequency transformer.

.By reason of the use of a WheatstOne bridge I am enabled to supply modulating potentials to the oscillatory system for the transmission of signals and to derive audio frequency potentials from the said system for the purpose of signal [reception without any interference between the two operations. 7

Specifically, I prefer to connect the plate 43 of a modulator tube 45 directly to a point 47 on the bridge which is symmetrical with respect to a point 49 thereon to which the cathode of the tube is connected through a coupling condenser 51, of relatively large size. The modulator tube may be supplied with input potentials from a microphone 53 of any desired type.

The input circuit of an aud'o frequency ampliconnected across the opposite points 5'? and 59 of the bridge, a blocking condenser 61, of large capacity, preferably being included in the connecting circuit. The amplifying tube may be of the same type as the tube used for modulating and, in fact, all of the tubes in the entire system may be similar and may be supplied with plate and filament potentials from the same sources although, for purposes of con- Qyenience, sources individual to the several tubes have been shown in the drawing. a

In the operation of my improved system the radio frequency input and output circuits of the push-pull stage are adjusted to substantial syngtony with the carrier-frequency at which it is desired to maintain duplex operation. In such event, the said stage oscillates vigorously and the several tubes therein draw a considerable amount of grid current. The grid current drawn by the .itiubes causes the grid condenser 15 to acquire a negative charge which tends to stop the oscillations or to materially reduce their amplitude.

If the system is permitted to oscillate freely, signal reception, except of continuous waves, is impeded. I, therefore, so adjust the grid biasing potential by movement of the potentiometer arm, by varying the magnitude of the grid leak 20, or by altering the capacity of the grid condenser 15, that the charge acquired by the said condenser shall leak off at a definite rate, preferably above audibility.

By adjustment of the grid condenser or the grid leak, or both, the leakage of the charge may be rendered discontinuous and may be given any desired periodicity from a succession of pulses at a rate of one or two per second, up to a frequency far beyond the limits of audibility.

When the rate of leakage is properly fixed, the system exhibits very remarkable sensitivity, insofar as signal reception is concerned, yet it is substantially immune to hand capacity effects.

Although the scope of my invention is not to be restricted by any theory of operation advanced herein, it is my present belief that the sensitivity may well be ascribed to the fact that the system has negative resistance, at least periodically, and that the signal builds up during these periods of negative resistance until it is of such amplitude that it is rectified by the thermionic tubes 1 and- 3, functioning in parallel. Theperiodicity of the negative resistance is introduced by the blocking action of the common grid condenser 15 and the grid leak 20, or by the action of the grid leak 20 alone, if the grid condenser is omitted, and is I influenced by the plate-circuit impedance.

At any rate, the system behaves as though the several thermionic tubes function in parallel to demodulate an incoming signal, since the demodulated signal appears across the choke coil 35 over which plate potential is supplied to the tubes.

As opposed to the theory outlined above, it is noted that when the variation frequency is brought into the region of audibility, it seems to be present with substantially unvarying amplitude in the output circuit, irrespective of the amplitude of the demodulated signal. It is highly probable, therefore, thatcertain additional phenomena are present during signal reception, the character of which I have not yet definitely determined.

It will be noted from an inspection of the drawing that the choke coil 35, through which plate potential is supplied to the'push-pull stage'and to the modulator tube, is the equivalent of the I modulation chokeemployed in the usual and well-known l-leising modulation system. The output at. radio frequency from the oscillator tubes, therefore, may be effectively modulated and, by reason of. the fact thatthe currents flowing in the input circuit of the push-pull stage are of substantial magnitude, quite :good radiation may be obtained from the antenna 17.

During the reception of signals the potentials at audio frequencies'which'appear across the choke.

coil 35 cause potentials to arise across the points 57 and 59 of the bridge, to which the input circuit of the amplifier device 55 is connected; In-

asmuch, however, as the potential of the points 57 and 59 does not materially change during the transmission of signals, the transmitted signals are substantially inaudible to the operator and do not cause any interference .with the reception of signals from a distant station.

In a commercial system constructed according to my invention, the four thermionic tubes'are of the type known as Radiotron 230, operating at a filament potential of two volts. tial supplied by the biasing Lbattery23 is substantially nine volts and th-eplate potential delivered by the source is in the neighborhood} of 135 volts. i'he variable grid leak 20 has a-resistance of the order of 150,600 ohms or more and the common grid condenser has a capacity of the order of substantially .00025 microfarads.

- The input and output inductors,for the satis'-- factory reception and transmission of signals at frequencies of the order of megacycles, each have an inductance equivalent to that of a coil comprising three or 'four'turns'of No. 8 B &'S gauge wire wound upon'a' form 1 in diameter, the turns being spaced apart and the four simultaneously adjustable tuning condensers each have a maximum capacity of 35 to 50 micromicrofarads.

It should be clearly understood that tubes of the three-electrode type have been chosen merely for purposes of illustration and that my invention is not restricted to their specific use. It should also be apparent that I may utilize individual grid condensers and grid leaks, either fixed or adjustable, in lieu of the common grid-com denser l5 and grid leak 20 shown. In the latter event, the input inductor may or may not be pr0-= vided with a connection to ground to establish an electrical center.

I wish also to point out that, in case individual grid condensers and grid leaks are employed, the grid leaks may either be connected in shunt to the respective grid condensers, or they may be connected in series across the grid terminals of the several tubes. When disposed directly across the grid terminals, the junction point of the grid leaks is, preferably, connected to the negative terminal of the grid biasing source through a variable resistor and, for microadjustment, a variable condenser may be connected in shunt to both the said variable resistor and the said source. By reason of the fact that the grid leaks, when they are disposed in shunt relation to the input inductor, exert a damping eifect, this arrangement oscillates less readily than the circuit first described, and is not considered by me to be especially suitable for transmitting or receiving on ultra-high frequencies. It does, however, give quite good results for frequencies of the order of 10 megacycles, and lower.

If portability is essential the entire system may be housed in a metal box to which one end of the coil 18 is connected. Signal reception and radiation may be had by disposing one end of a Small exterior loop-shape antenna in capacitive relation to the box, the other end extending into the interior thereof and being connected to the otherwise free end of the coil 18. The radiating System is then complete and is in effect a dipole, one side of which is the metal box, the other side being the extending wire.

The variation frequency, during use of the system as a transmitter, seems to have no particularly deleterious effect. It may, however, be prevented from being developed by reducing the resistance of the leak resistor 20 or by manually manipulating the switch 16 to disconnect the grid condenser 15 from the circuit.

It will be apparent from consideration of the foregoing description of my improved duplex radio system that it has numerous advantages. I am aware that it has previously been pro- The poten-' posed to attain duplex operation by employing switching means which, when operated, disconnect the antenna from the receiver and connect it to the transmitter, and vice versa, the oscillations being-reduced in amplitude during the reception periods to such an extent that they may be utilized for heterodyning an incoming signal in a separate receiver. Insofar as I am aware, however, my-improved system is the first wherein no attempt is made to reduce the oscillations during the reception of signals and wherein the oscillator'tubes function simultaneously for the reception and transmission of signals without interference between the several functions.

Althoughl have illustrated a specific embodi ment of my inventiornand have described certain variants thereof, numerous other modifications will be apparent to those skilled in the art. My invention, therefore, is not to be restricted except insofar as is necessitated by the prior art and by the spirit of the appended claims.

I claim as my invention:

1. A signaling system including a thermionic tube, means for causing said tube to generate oscillations, and means whereby said oscillations, without change in the normal amplitude thereof, may be utilized for both transmission and reception of intelligence, said means including a Wheatstone bridge circuit for supplying modulating potentials to said oscillatory system and ligence, said means including an anode supply circuit and a balanced electrical bridge circuit, one arm of which bridge circuit is included in said supply circuit, and means whereby said oscillations cooperate with an incoming signal to permit the reception of intelligence through said ibridge circuit.

3. A super-regenerative signal-receiving system including a thermionic oscillator having an output circuit in combination with means. whereby said system may be employed for the transmission of signals, said means including a modulating device, an amplifying device, and a balanced electrical bridge circuit interposed between said output circuit and said devices.

4. A super-regenerative receiving system in combination with means whereby said system may be employed for the transmission of signals and further characterized in that means including a balanced electrical bridge circuit, are provided for preventing transmitted signals from interfering with the reception of signals from adistant station.

5. The combination as set forth in claim 4 wherein one arm of the bridge circuit is used as a modulation-choke.

6. A thermionic tube having input and output circuits inter-coupled regeneratively, a modulator, an amplifier, and means including a balanced electrical bridge circuit, for coupling said modulator and amplifier to said output circuit. 150

7. The combination as set forthin claim; 6 further characterized in that the modulator and amplifier are connected, respectively, to homologous points on said bridge circuit.

8. The combination as set forth in claim G wherein one of the arms of said bridge circuit constitutes a modulation choke.-

9. In a signaling system, the combination of an oscillation generator including a thermionic tube having an output circuit, electrical impedance means providing a balanced electrical bridge circuit through a portion of which said output circuit is connected, a signal modulating circuit connected at two electrically opposite points on said bridge circuit, and a signal receiving and amplifying circuit connected at two other electrically' opposite points on said bridge circuit, whereby interactionbetween said modulator andamplifier circuits is prevented.

10. In a signaling system, the combination of an oscillation generator including a pair of push pull connected thermionic tubes, a circuit for supplying anode potentials thereto, an electrical im-' pedance device in said circuit, electrical circuit impedance means connected with said impedance device: to provide a balancedelectrical bridge circuit, a modulator tube having anode and cathode connections with the bridge circuit at points elec trically symmetrical with respect to each other, and a signal amplifier device connected across two other opposite points on said bridge circuit.

' CARLETON D. HAIGIS. 

